Manufacturing process of thin film transistor array substrates is complex, in general, the manufacturing process comprises depositing a metal film and a semiconductor film on a base substrate, then forming a required metal pattern (for example, a pattern of gate lines, a pattern of data lines and a pattern of common electrode lines) and a semiconductor pattern (for example, an active layer) by a patterning process. In a case of forming a signal line, a circuit of the signal line needs to be tested. Each of the thin film transistor array substrates comprises a large number of parallel wirings, so that open circuit, short-circuit between films and other undesirable phenomena are prone to be occurred due to photoresist residue, static electricity and metal residues among the parallel wirings.